Surveillance cameras are widely used as an aid in providing physical security for employees and property, such as commercial, industrial and government facilities. In many instances, the images from the camera are simply viewed in real-time by security guards.
It is also common to record the output of each camera on a time-lapse video cassette recorder (VCR). In the event of a problem or security incident, the resulting recording can then be examined. It is also possible to use a video or infrared motion detector, so that the VCR does not record anything except when there is motion in the observed area. This reduces the consumption of tape and makes it easier to find footage of interest. Nevertheless, it does not eliminate the need for the VCR, which is a relatively complex and expensive component that is subject to mechanical failure and that requires periodic maintenance, such as cleaning of the video heads. Moreover, infrared motion detectors have a tendency to produce false detections.
Another known approach is to use an all-digital video imaging system, which converts each video image to a compressed digital form immediately upon capture. The digital data is then saved in a conventional database (such as a disk farm backed up by a tape juke box). This approach is relatively expensive, requires a substantial amount of storage space, and does nothing to help an operator find frames of interest.
Another approach uses a video camera and personal computer to detect and track people, and saves the first image that satisfies some alarm condition. However, this system makes no attempt to select a good view of the person, as a result of which the saved image may show the person with his or her back to the camera, rendering it difficult or impossible to identify the particular person. Another known system displays a path of movement of a detected person who is in the observed area, but discards the path of movement after the person leaves the observed area.
All of these known approaches have been generally adequate for their intended purposes, but they have not been satisfactory in all respects. For example, they involve hardware which is relatively expensive and not particularly compact. They often use a VCR, which is subject to mechanical failure and requires periodic maintenance. Some systems store all incoming video information, which uses a substantial amount of storage capacity, and makes it difficult to find of events of interest.